Project Summary/Abstract The proposed project will use a multi-site within-school randomized control trial (RCT) intervention design to promote positive intergroup relationships and to reduce prejudice in childhood. The health consequences for children who experience discrimination (e.g., name-calling, bullying, exclusion) as a result of prejudice include compromised health and well-being, stress and anxiety, and social withdrawal. Further, individuals who perpetuate bias (i.e., hold biases about social groups that restrict their social interactions) also experience health-related stress associated with negative intergroup relationships in school settings. Thus, reducing prejudice and bias in childhood has positive health, attitudinal, and academic outcomes for all children. Extensive developmental science research has shown that implicit bias (negative attitudes toward other social groups of which the beholder is unaware) and explicit biases (stereotypes) emerge as early as the preschool period and become more pervasive by late childhood, particularly as justifications for social exclusion. Research has provided evidence that positive contact with peers from different ethnic, racial, and cultural backgrounds effectively reduces prejudice and bias. Given the prevalence of bias-based social exclusion among children, the goal of the project is to promote positive intergroup contact and reduce biases and stereotypes in childhood. Participants will be 3rd, 4th, and 5th grade students (8 ? 11 years of age; N = 1,440) in 72 classrooms in 12 schools in a large public school district outside of a large metropolitan area. The sample will be racially and ethnically diverse and include European-American, African-American, Latino/a, Asian- American, and multiracial students, who will be randomly assigned to an intervention program or a control condition (Business-as-Usual). The 10-week program involves the use of an in-classroom web-based curriculum tool called Developing Inclusive Youth, in conjunction with teacher-led classroom discussion sessions. Children make decisions and observe the outcomes of their own decision-making as the action unfolds contingent on their inclusion or exclusion choice while using the app. The pre-test post-test measures include socioemotional (school belonging, peer and teacher support, ethnic and gender public regard) and intergroup attitudes (social exclusion evaluations, and diversity in friendship choices). Analyses will utilize mixed modeling using restricted maximum likelihood estimation. We expect that, compared to the control group, children in the intervention program will have higher socioemotional scores and lower intergroup bias scores following the intervention. The benefits of decreasing prejudiced attitudes will be promotion of healthy social and emotional development of children.